Allergic diseases such as asthma are research epidemic proportions in the industrialized and developing world. Major factors driving these rising trends are increased exposure to sensitizing allergens and reduced stimulation of the immune system during critical periods of development. In allergic disease, reduced stimulation of the immune system during critical periods of development. In allergic disease, there is a polarization of T-lymphocyte responses, and enhanced secretion of cytokines involved in regulation of immunoglobulin E, mast cells, basophils and eosinophils, ultimately leading to inflammation and disease. The hygiene hypothesis suggests that early exposure to microorganisms stimulates the immune system to prevent this type of polarization and thereby inhibits the development of allergies. The central hypothesis of this proposal is that triggering the immune response through the Toll-like receptors, which bind to microbial products, establishes an immunologic window that preferentially differentiates T cells to a non-allergic phenotype and maintains this memory. We propose 1) to evaluate the role of TLR signaling in priming of the adaptive immune responses; 2) to determine the role of TLRs in the effector phase of the immune response; and 3) to evaluate the immunologic function of mice generated in Project 1 with novel germline mutations in rendering them resistant to ISS and/or LPS treatment. A clear understanding of the cellular and molecular mechanisms of allergic disease and the complex interplay between genetic and environmental factors may potentially identify new molecular targets for therapeutic interventions.